System and method for enhanced metal recovery during atmospheric leaching of metal sulfides

ABSTRACT

A method of improving metal leach kinetics and recovery during atmospheric or substantially atmospheric leaching of a metal sulfide is disclosed. In some embodiments, the method may comprise the steps of: (a) producing a metal sulfide flotation concentrate; (b) processing the metal sulfide concentrate in a reductive activation circuit that operates at a first redox potential, to produce a reductively-activated metal sulfide concentrate; and, (c) subsequently processing the activated metal sulfide concentrate in an oxidative leach circuit to extract metal values. In some disclosed embodiments, reductive activation steps may be employed prior to oxidative leaching steps (including heap leap leaching or bio-leaching steps). In some embodiments, physico-chemical processing steps may be employed during reductive activation and/or oxidative leaching. Systems for practicing the aforementioned methods are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National stage § 371 application ofPCT/US2015/050045, filed on 14 Sep. 2015, which claims priority to andthe benefit of U.S. Provisional Patent Application No. 62/050,039, filedon Sep. 12, 2014 and titled “SYSTEM AND METHOD FOR ENHANCED METALRECOVERY DURING ATMOSPHERIC LEACHING OF METAL SULFIDES.” The contents ofthe aforementioned applications are hereby incorporated by reference intheir entirety for any and all purposes as if fully set forth herein.

FIELD OF THE INVENTION

Embodiments of the invention relate to equipment, flowsheets, andprocesses for improving metal value extraction from metal sulfide ores.In particular, systems and methods for increasing metal recovery withinan atmospheric, or substantially atmospheric, oxidative leach isdisclosed. Also disclosed, are systems and methods for increasing metalrecovery during heap leaching of metal sulfides.

BACKGROUND OF THE INVENTION

Current and past methods of atmospheric leaching of primary metalsulfides (e.g., Chalcopyrite, Tennantite, and Enargite), may suffer fromslow reaction kinetics and poor metal recoveries due to surfacepassivation effects during oxidative leaching. Surface passivationoccurs when the growth of an elemental sulfur product layer occludes thesurfaces of the particles being leached. The sulfur reaction productlayer acts as a physical barrier, impeding the transport of reactantsand products from the reaction plane.

A number of factors may enhance the detrimental effects of the sulfurproduct, with regard to metal dissolution, by altering the porosityand/or tortuosity of the product layer. These factors, individually orcollectively, include crystal phase transformations, partial melting andrecrystallization, or complete crystal melting. The range of passivationeffects will depend upon the temperature of the reaction medium and thetemperature at the reaction zone which may be different from the overallsystem temperature. This temperature difference may be sustainedthroughout the entire leach process or it may be transitory.

Other mechanisms of passivation can include the formation ofnon-stoichiometric, metal-deficient sulfide phases that are resistanttoward further anodic dissolution reactions. Furthermore, if thedissolution of the metal sulfide is taking place via an electrochemicalredox mechanism, the anodic dissolution step will be dependent upon thepH and redox potential at the reaction plane.

A number of factors, known to those skilled in the art, can make itdifficult to maintain an optimum redox potential and thereby achievecomplete metal recovery at maximum dissolution rates. In some instances,leaching of primary metal sulfides may also suffer from slow reactionkinetics and poor metal recoveries due to residual frothing agents usedduring froth flotation. The residual frothing agents may be present onparticles being leached and interfere with superficial leachingchemistries.

A number of past methods have been attempted to increase metal leachrates by employing leach catalysts. One approach suggested addressingthe passivation issue by increasing electron transport though anelectrically-resistive, reaction-product layer by doping the layer withfine particulate carbon (see for example U.S. Pat. No. 4,343,773).Moreover, a more recently-proposed method (US-2012/0279357) foraddressing passivation relies on the addition of an activated carboncatalyst to enhance the leach rate of arsenic-containing coppersulfides. Still other approaches have used silver-based catalytic leachsystems for enhancing the copper dissolution rates in acidic ferricsulfate media (J. D. Miller, P. J. McDonough and P. J. Portillo,Electrochemistry in Silver Catalyzed Ferric Sulfate Leaching ofChalcopyrite, in Process and Fundamental Considerations of SelectedHydrometallurgical Systems, M. C. Kuhn, Ed., SME-AIME, New York, pp.327-338, 1981), while others have used silver-activated pyrite toaccomplish similar results (U.S. Pat. No. 8,795,612). The Applicant hasfurther recently proposed a method and process for the enhanced leachingof copper-bearing sulfide minerals which utilizes microwave irradiationduring leaching to combat the adverse effects of passivation on leaching(WO2014074985 A1).

Still others have adopted pre-leach ultra-fine grinding (i.e.,mechanical activation) of a copper sulfide concentrate to achieve rapidpost-grinding leach kinetics. U.S. Pat. No. 5,993,635 describes a methodfor recovering copper from sulfide-mineral compositions which comprisesthe step of ultra-fine grinding of the leach feed to a P80 of about 5 μm(see Example 3 in U.S. Pat. No. 5,993,635). While copper dissolutions of95% or greater were achieved in 10 hours on a small scale, grinding tosuch a small particle size prior to leaching is not always economicallyin those cases where the leach feed is a low-grade metal concentrate.

Still others have combined ultra-fine grinding and leaching in so-calledbatch Mechano-Chemical leaching processes which are circular batchprocesses which do not provide for continuous downstream flow. Moreover,all prior art methods have required excessively large energy inputs toachieve significant levels of copper dissolution from chalcopyrite.While leach times to achieve 80% copper extraction have beendemonstrated to be as short as 1 hour, the approach is difficult toadapt for large-scale commercial operation (D. A. Rice, J. R. Cobble,and D. R. Brooks, Effects of Turbo-milling Parameters on theSimultaneous Grinding and Ferric Sulfate Leaching of Chalcopyrite, RI9351, US Bureau of Mines, 1991). Furthermore, copper recoveries inexcess of 95-97% were not achievable due to passivation at highelemental sulfur loading.

As previously stated, the application and consumption of large specificenergy renders the economic feasibility of full-scale industrial metalrecovery in mechano-chemical processes impractical.

OBJECTS OF THE INVENTION

It is, therefore, an object of some embodiments, to improve leachkinetics and metal recovery through the employment of a reductiveactivation step prior to oxidative leaching. The oxidative leach ispreferably performed in an atmospheric or substantially atmosphericmetal sulfide leach circuit.

It is also an object of some embodiments, to reduce and/or eliminate theneed for the addition of a superfluous reagent or reagents into theleach circuit, which might cost additional money to purchase, ship, anddose; and/or which might negatively impact downstream SX/EW systems.

It is a further object of some embodiments, to provide a reductiveactivation prior to an oxidative leach process. The reductive activationinduces lattice strain and alters the electrochemical properties withinthe leach particles by conversion to one or more transitory, metastable,non-stoichiometric binary metal sulfide phases.

According to yet further objects of some embodiments, the efficiency ofheap leach operations may be improved by reductively treating an oreprior to heap leaching or after ore stacking but prior to oxidativeleaching.

According to yet further objects of some embodiments, the efficiency ofbio-leaching operations may be improved by reductively treating an oreprior to bio-leaching to produce lattice transformations and/or latticestrain via production of a metastable non-stoichiometric binary metalsulfide phase.

According to yet further objects of some embodiments, the efficiency oftank or vat leaching operations may be improved by reductivelyactivating an ore prior to tank or vat leaching.

Yet another object of some embodiments, is to mitigate the effects ofmechanical and/or electrochemical passivation by employing activationtechniques prior to oxidative leaching (e.g., via reductive activation).

It is another object of some embodiments to mitigate the effects ofmechanical and/or electrochemical passivation by employingmechano-chemical/physico-chemical activation techniques during oxidativeleaching.

These and other objects of the present invention will be apparent fromthe drawings and description herein. Although every object of theinvention is believed to be attained by at least one embodiment of theinvention, there is not necessarily any one embodiment of the inventionthat achieves all of the objects of the invention.

SUMMARY OF THE INVENTION

A method of improving metal leach kinetics and metal recovery duringatmospheric or substantially atmospheric leaching of a metal sulfide isdisclosed. The method may, in some embodiments, comprise the steps of:(a) producing a flotation concentrate; (b) processing the concentrateunder reductive conditions to produce an activated concentrate; and, (c)subsequently processing the activated concentrate by oxidativedissolution to extract metal values.

In some embodiments, the reductively-activated concentrate may compriseparticles composed of chalcopyrite, and impurities therein may comprisepyrite and silicates. In some embodiments, the activated concentrate mayfurther comprise molybdenite and/or precious metals.

The method may further comprise the step of subjecting the activatedconcentrate to an oxidative leach process as described in step (c). Insome embodiments, the activated concentrate may comprise chalcopyriteparticles having an outer covellite-like mineral phase.

In some embodiments, the time to achieve greater than 95% extraction ofmetal values from the activated concentrate via oxidative dissolutionmay be less than 6 hours. In some embodiments, the time to achievegreater than 95% metal extraction by oxidative dissolution may be lessthan 5 hours, or between 2.5 and 4 hours.

In some embodiments, the reductive activation circuit may comprise oneor more of the following: stirred tank reactors, shear tank reactors,and various combinations thereof.

In some embodiments, the reductive activation circuit may be maintainedat a redox potential between 200 mV (SHE) and 650 mV (SHE), for example,between 200 mV (SHE) and 450 mV (SHE). In some embodiments, theoxidative leach circuit may be maintained at a redox potential between600 mV (SHE) and 800 mV (SHE), for example, between 650 mV (SHE) and 750mV (SHE).

In some embodiments, the step of oxidatively leaching the activatedconcentrate may further comprise the combination of a plurality ofstirred-tank reactors with one or more shear-tank reactors. In someembodiments, the oxidative leach reactors may be arranged in series withthe shear-tank reactor(s). In some embodiments, the oxidative,stirred-tank reactors may be arranged in parallel with the shear-tankreactors. In some embodiments, the oxidative, stirred-tank reactors maybe arranged in series and in parallel with the shear-tank reactor(s).

In some embodiments, a single shear-tank reactor may be shared betweenmultiple, oxidative stirred-tank reactors. In some embodiments, themethod may further comprise converting/transforming a substantialportion of the metal sulfide particles within the metal sulfideconcentrate to an activated mineral phase using at least one reductiveactivation reactor.

A metal recovery flowsheet is also disclosed. The metal recoveryflowsheet may comprise: (a) a sulfide concentrator comprising aflotation circuit to produce a metal sulfide concentrate; and (b) anatmospheric, or substantially atmospheric, metal sulfide leach circuit.The atmospheric, or substantially atmospheric, metal sulfide leachcircuit may comprise: (i.) a reductive activation process, (ii.) and asubsequent oxidative leach process for recovering at least one metalvalue from the activated concentrate via dissolution.

In some embodiments, the reductive activation circuit may be maintainedat a redox potential between 200 mV (SHE) and 650 mV (SHE) with pHcontrol, and the combination of pH and redox maintained in such a mannerto produce the reductively-activated metal sulfide product.

In some embodiments, the oxidative leach circuit may be maintained at apH below about 1.0 and a redox potential between 600 mV (SHE) and 800 mV(SHE), or at a combined pH of less than about 1.0 and a higher redoxpotential than the redox potential of the reductive activation circuit.In some embodiments, the flowsheet may further comprise one orshear-tank reactors operatively connected to a plurality of oxidative,stirred-tank reactors.

A method of extracting a metal from a metal sulfide particle is furtherdisclosed. According to some preferred embodiments, the method maycomprise the steps of: (reductively) activating a metal sulfide particleby a copper metathesis reaction thereby changing a portion of the metalsulfide particle from a primary metal sulfide to a non-stoichiometric,metastable binary-metal sulfide phase; and extracting a metal from theactivated, metal sulfide particle. The conversion to a metastablenon-stoichiometric binary metal sulfide phase is carried out so as tointroduce point defects substantially throughout the entirety of theactivated particle.

According to some preferred embodiments, the step of extracting themetal from the activated, metal sulfide particle may comprise anoxidative leaching process. According to some embodiments, the portionof the metal sulfide particle changed to the transitionary,non-stoichiometric, metastable binary-metal sulfide phase via a coppermetathesis may be less than about one-half of the metal sulfide particleby weight or less than about one-half by volume. In yet otherembodiments, the portion of the metal sulfide particle that is changedmay amount to less than about one fourth of the metal sulfide particleby weight or less than about one fourth by volume. In still furtherembodiments, the portion of the metal sulfide particle that is changedmay be less than about one tenth of the metal sulfide particle by weightor less than about one tenth by volume, for example around 2-8% of theparticle by weight or volume, without limitation.

According to some embodiments, the step of activating the metal sulfideparticle may be performed in a reductive environment ranging from about200 to about 650 mV (SHE) with simultaneous pH control. According tosome embodiments, the step of extracting the metal after reductivepre-treatment/activation of the metal sulfide particle may be performedby a heap leaching process, a vat leaching process, a tank leachingprocess, a dump leaching process, a bio-leaching process, or acombination thereof, without limitation; wherein the transitionarynon-stoichiometric, metastable binary metal sulfide phase may improveleach kinetics and/or recovery of the metal.

In some embodiments, the method may further comprise the steps of: priorto the activation, analyzing a metal sulfide concentrate in order todetermine whether passivating secondary metal sulfide rimming is presentin an amount sufficient to inhibit activation of the metal sulfideparticles; and subsequently decreasing a mean particle size of theconcentrate to a sufficient degree if it is determined that the amountof passivating secondary metal sulfide rimming is sufficient to inhibitactivation of the metal sulfide particles. In this regard, theactivation step may be optimized and liberation of the metal from themetal sulfide particles may be improved. According to some embodiments,the step of analyzing the metal sulfide concentrate may be performedusing a mineral analyzer. According to some embodiments, the method mayfurther comprise the step of performing particle mapping or liberationanalysis using data collected by the mineral analyzer. According to someembodiments, the step of decreasing the mean particle size may comprisegrinding until the amount of passivating secondary metal sulfide rimmingis less than about 25%. According to some embodiments, the step ofdecreasing the mean particle size may comprise grinding until the amountof passivating secondary metal sulfide rimming is less than about 10%.According to some embodiments, the step of decreasing the mean particlesize may comprise grinding until the amount of passivating secondarymetal sulfide rimming is less than about 5%. According to someembodiments, more than about 5% of a surface of the primary metalsulfide may contain the passivating secondary metal sulfide rimming.According to some embodiments, more than about 10% of a surface of theprimary metal sulfide may contain the passivating secondary metalsulfide rimming. According to some embodiments, more than about 25% of asurface of the primary metal sulfide may contain the passivatingsecondary metal sulfide rimming. According to some embodiments, theprimary metal sulfide phase may comprise chalcopyrite.

A method of leaching a metal sulfide concentrate is further disclosed.The method preferably comprises the steps of: processing a metal sulfideconcentrate at a first redox potential to produce areductively-activated metal sulfide concentrate comprising anon-stoichiometric metastable (e.g., transitionary) binary metal sulfidephase; and leaching a metal from the reductively-processed metal sulfideconcentrate via oxidative dissolution.

According to some embodiments, the non-stoichiometric metastablebinary-metal sulfide phase comprises less than about 50 wt. % or lessthan about 50 vol. % of the activated particle. According to someembodiments, the non-stoichiometric metastable binary metal sulfidephase comprises less than about 25 wt. % or less than about 25 vol. % ofthe activated particle. According to some embodiments, thenon-stoichiometric metastable binary metal sulfide phase comprises lessthan about 10 wt. % or less than about 10 vol. % of the activatedparticle.

According to some embodiments, the oxidative dissolution occurs in anoxidative stirred-tank reactor at a second redox potential greater thana rest potential of the activated particle. According to someembodiments, the first redox potential ranges from about 200 to about650 mV (SHE). According to some embodiments, the second redox potentialranges from about 600 to about 800 mV (SHE).

According to some embodiments, the metal sulfide concentrate compriseschalcopyrite. According to some embodiments, the oxidative dissolutionis carried out in a shear-tank reactor; wherein reactor may be selectedfrom at least one of the group consisting of: a stirred media reactor(i.e., SMRt reactor), a high-shear stirred reactor comprising one ormore high-shear impellers and/or pumping blades, and a high-shearreactor comprising a high shear rotor and stator.

According to some embodiments, the method may further comprise leachinggreater than 80% metal in under about 6 hours by operating theshear-tank reactor at a power density ranging from about 2 kilowatts percubic meter to about 100 kilowatts per cubic meter. According to someembodiments, the method may comprise leaching greater than 95% metal inunder about 6 hours by operating the shear-tank reactor at a powerdensity ranging from about 5 kilowatts per cubic meter to about 100kilowatts per cubic meter.

According to some embodiments, the method may comprise leaching greaterthan 98% metal in under about 6 hours by operating the shear-tankreactor at a power density ranging from about 5 kilowatts per cubicmeter to about 20 kilowatts per cubic meter. According to someembodiments, the method may comprise leaching greater than 95% metal inunder about 6 hours by operating the shear-tank reactor at a powerdensity ranging from about 20 kilowatts per cubic meter to about 100kilowatts per cubic meter. In some preferable embodiments, the metalleached from the metal sulfide is copper.

A method of extracting a metal from a metal sulfide particle is furtherdisclosed. The method may comprise the steps of: activating a metalsulfide particle by changing a portion of the metal sulfide particlefrom a primary metal sulfide to an activated binary metal sulfide phase;followed by extracting a metal from the activated metal sulfide by anoxidative leach process.

According to some preferred embodiments, the oxidative leaching of theactivated metal sulfide particles may be further enhanced by aphysico-chemical process. The process may comprise an oxidative leach ofa metal sulfide particle that substantially reduces both theelectrochemical passivation and mechanical passivation of a metalsulfide particle via a physico-chemical mechanism. According to someembodiments, the physico-chemical mechanism may comprise the use of ashearing process and a stirred-tank leaching process. According to someembodiments, the shearing process may comprise mechanical scrubbing,grinding, attrition, or a combination thereof. According to someembodiments, the shearing process may use shear-tank reactor, which isselected from at least one of the group consisting of: a stirred mediareactor (SMRt reactor), a high-shear, stirred reactor comprising one ormore high shear impellers and/or pumping blades, and a high-shearreactor comprising a high-shear rotor and stator. According to someembodiments, said shearing process may be performed after thestirred-tank leaching process. According to some embodiments, saidshearing process is performed before the stirred-tank leaching process.According to some embodiments, said shearing process may be performed inseries and/or in parallel with the stirred-tank leaching process.According to some embodiments, said stirred-tank leaching process andsaid shear tank reactor(s) may be performed via a flow-throughcontinuous linear process.

According to some embodiments, the stirred-tank reactors may be operatedunder atmospheric pressure and the shear-tank reactors may besubstantially operated above atmospheric pressure or at atmosphericpressure.

According to some embodiments, the shear-tank reactors may be operatedat an oxygen overpressure pressure ranging from about 1 to about 10 bar.According to some embodiments, the metal sulfide particles may spendgreater than about 80-95% of their collective residence time within thestirred-tank reactors. According to some embodiments, the metal sulfideparticles may spend less than about 10-20% of their collective residencetime within the shear tank reactors. According to some embodiments, theshearing process may comprise controlling both the pH and redoxpotential simultaneously by using acid, ferric iron, gaseous O₂, air, ora combination thereof.

According to some embodiments a wetting agent may be used to controlfrothing. The wetting agent may comprise one or more of a polymericelectrolyte, a polymeric flocculant, or a variety of polymericelectrolytes and polymeric flocculants.

According to some embodiments, a wetting agent may be advantageouslyused to reduce the amount of residual metal in the leach tailings fromthe oxidative leach process to less than 1 wt. %, more advantageously toless than 0.8 wt. % and more advantageously to less than 0.5 wt. %.

According to some embodiments, one or more shear-tank reactors may beoperatively coupled to a plurality of stirred-tank reactors, wherein acollective residence time of the metal sulfide particles in the one ormore shear-tank reactors may depend upon overall residence time withinthe oxidative leach process. The residence time within the one or moreshear-tank reactors will also depend upon the volumetric ratio betweenthe combined volume of the stirred-tank reactor(s) and the combinedvolume of the shear reactors. The preferred volumetric ratio is notequal to one. According to some embodiments, the volumetric ratio of theshear-tank reactor(s) to the stirred-tank reactor(s) may be betweenabout 1:10 and about 1:150.

According to some embodiments, about 90% or greater metal recovery maybe achieved in less than 10 hours while operating at a temperature belowthe melting point of elemental sulfur. According to some embodiments,the process may further comprise ultra-fine grinding of the concentrateprior to reductive activation and oxidative leaching to a P95 of 40microns or finer.

BRIEF DESCRIPTION OF THE DRAWINGS

To complement the description which is being made, and for the purposeof aiding to better understand the features of the invention, a set ofdrawings illustrating preferred processing apparatus and methods ofusing the same is attached to the present specification as an integralpart thereof, in which the following are depicted as illustrative andnon-limiting character. It should be understood that like referencenumbers used in the drawings (if any are used) may identify likecomponents.

FIG. 1 is a schematic diagram illustrating a non-limiting, exemplaryflowsheet which might employ certain embodiments of the invention.

FIG. 2 is a schematic diagram illustrating, in more detail, a portion ofthe non-limiting, exemplary flowsheet shown in FIG. 1, wherein areductive activation/pretreatment step may be performed prior to anoxidative atmospheric (or substantially atmospheric) metal sulfide leachprocess.

FIG. 3 is a schematic diagram illustrating a system and method ofproviding a reductive activation step prior to an oxidative atmospheric(or substantially atmospheric) metal sulfide leach, according to someembodiments.

FIG. 4 is a schematic diagram illustrating a system and method of usinga reductive activation and/or a reductive pre-treatment step which maybe employed in heap leach operations.

FIG. 5 suggests a method for enhancing metal recovery from metalsulfides and/or for enhancing leach kinetics of metal sulfides accordingto some embodiments which may be utilized for various forms of leachingincluding, but not limited to, vat leaching, tank leaching, heapleaching, bio-leaching, and/or the like, without limitation.

FIG. 6 suggests a method for enhancing metal recovery from metalsulfides and/or for enhancing leach kinetics of metal sulfides accordingto some embodiments; particularly for leaching metal sulfideconcentrates.

FIG. 7 suggests a method for enhancing metal recovery from metalsulfides and/or for enhancing leach kinetics of metal sulfides accordingto some embodiments; particularly for heap leaching metal sulfide ores.

FIG. 8 suggests several exemplary and non-limiting arrangements ofshear-tank reactors and a plurality of stirred-tank reactors within anoxidative metal sulfide leach circuit. It should be understood that theparticular arrangement depicted in FIG. 8 has been provided merely toillustrate several different possible cooperative structuralrelationships between shear-tank reactors and stirred-tank reactorswithin the same figure, and therefore, variant embodiments should not belimited to the particular configuration shown. Accordingly, anticipatedembodiments may practice as little as one of the particularconfigurations shown; anticipated embodiments may practice more than oneof the particular configurations shown; anticipated embodiments maycontain any pattern or sequence of the particular configurations shown;and anticipated embodiments may contain one or more of the particularconfigurations redundantly, without limitation.

In the following, the invention will be described in more detail withreference to drawings in conjunction with exemplary non-limitingembodiments.

DETAILED DESCRIPTION OF THE INVENTION

The following description of the non-limiting embodiments shown in thedrawings is merely exemplary in nature and is in no way intended tolimit the inventions disclosed herein, their applications, or uses.

As schematically shown in FIG. 1, embodiments of the invention maycomprise a metal recovery flowsheet 10 having a unit operation 12. Theunit operation 12 may comprise an atmospheric or substantiallyatmospheric metal sulfide leach circuit 200 downstream of a sulfideconcentrator circuit 100, without limitation. Peripheral flowsheetoperations, typical to such processes known to those skilled in the artof minerals processing, are not shown.

In some preferred embodiments, most or all of the oxidative leaching mayoccur at atmospheric pressure conditions. In some embodiments, a smallamount of oxidative leaching (e.g., leaching occurring within one ormore optional, but preferred shear-tank reactors) may occur atatmospheric conditions or optionally above atmospheric conditions.

In some preferred embodiments, a majority of the cumulative leachingtime may occur at atmospheric pressure conditions, and a minimal amountof cumulative leaching time may occur above atmospheric conditions. Forexample, in some non-limiting embodiments, an oxidative leach reactor202, such as the one shown in FIGS. 2, 3, and 8, may comprise one ormore continuous stirred-tank reactors (CSTRs). The shear-tank reactorsmay comprise one or more enclosed stirred media reactors which arepreferably configured to be pressurized (e.g., to 1-20 bar, 1-10 bar,1-5 bar, approximately 5 bar, or the like), receive oxygen, an oxygencontaining gas, and/or contain grinding media, without limitation.

In some embodiments, a shear-tank reactor 212 may comprise one or moreenclosed high shear stirred reactors configured to be pressurized (e.g.,to 1-20 bar, 1-10 bar, 1-5 bar, approximately 5 bar, or the like),receive oxygen, and/or impart shear by using one or more high shearimpellers and/or pumping blades, without limitation. In someembodiments, the high shear impellers may be selected from the groupconsisting of: a Cowles disperser blade, a sawblade mixing impeller, adispersion blade, a saw tooth dispersion blade, an angled tooth blade,an ultra-shear dispersion blade, a high-flow dispersion blade, arotor/stator, and a combination thereof, without limitation.

In some embodiments, the plurality of oxidative leach reactors 202 maybe operatively coupled to a shear-tank reactor 212 in parallel, inseries, or a combination thereof (as suggested in FIG. 8). In somepreferred embodiments, a shear-tank reactor 212 is placed in series,i.e., interposed between two oxidative, stirred tank reactors 202.

In some preferred embodiments, the volume of a shear-tank reactor 212may be relatively less than the volume of an oxidative stirred tankreactor 202. In some preferred embodiments, the energy consumed by ashear-tank reactor 212 may be relatively more than the energy consumedby an oxidative stirred tank reactor 202.

In some embodiments (not shown), the one or more shear-tank reactors 212may be omitted from the atmospheric or substantially atmospheric metalsulfide leach circuit 200 altogether. This arrangement can beadvantageously used in those cases where a high-grade concentrate isfirst ground to an ultra-fine size distribution prior to reductiveactivation and downstream oxidative leaching.

If one or more separate shear-tank reactors 212 are utilized incombination with a plurality of oxidative stirred-tank reactors 202,then slurry recycle may be employed within the oxidative leach process.

Dissolved copper is provided to enable the reductive activation processto proceed. The amount of dissolved copper provided should be sufficientto complete the desired degree of conversion from the primary metalsulfide to the metastable, non-stoichiometric binary metal sulfide. Theresidence time required to complete the activation processing istypically between approximately 5 and 60 minutes. For example, aresidence time of approximately 10-45 minutes, or a residence time ofapproximately 15-30 minutes, such as 20 minutes, may be sufficient priorto moving on to a downstream oxidative leach step. The activated metalsulfide concentrate 116 may be optionally re-ground in step 216, or sentdirectly to an oxidative leach circuit 202.

Pregnant leach solution (PLS) 204 created during the atmospheric orsubstantially atmospheric leaching of the metal sulfide concentrate 116may be sent from the oxidative leach circuit 200 to a downstream solventextraction/electrowinning (SX/EW) circuit, or direct electrowinning(D/EW) process.

Raffinate 206 may be recycled from the respective downstream solventextraction/electrowinning (SX/EW) circuit, or direct electrowinning(D/EW) processes, and sent back to the oxidative leach circuit 200.Leach residues formed within the atmospheric or substantiallyatmospheric metal sulfide leach circuit 200 may be sent to a preciousmetals recovery circuit and/or ultimately to a leach residues disposalarea as suggested by FIG. 1. While not expressly shown, leach residuesulfur may be internally or externally processed/recovered/removed, inorder to create sulfuric acid which can re-supply the leach processeswithin the metal recovery flowsheet 10, such as the activation circuit220 and/or the oxidative 202 leach circuit. Manufactured sulfuric acidproduced from the elemental sulfur may also be sent to another unitoperation(s), or may be sold or distributed outside of the flowsheet 10,as a salable byproduct to help offset flowsheet 10 operating costs.

In some embodiments, a bleed stream 233 may be separated from the mainflow of reductive activated product 231 as shown in FIG. 3. The bleedstream 233 enters a solid/liquid separation circuit 222 which maycomprise equipment such as a filter, thickener, centrifuge, cyclone,dewatering screen, or the like, without limitation. The solid fraction224 leaving the solid/liquid separation circuit 222 may be recombinedwith the activated concentrate to be processed in the oxidative leachcircuit 202. The liquid fraction 226 leaving the solid/liquid separationcircuit 222 may enter one or more downstream processes for recoveringother metals, or impurities removal, without limitation.

“Reductive activation”, where described herein, may comprise anymetathesis or pre-treatment step, process, system, or device which iscapable of converting at least a portion of a leach particle from afirst mineral phase to a transitionary mineral phase. For example, a“reductive activation” pretreatment step or circuit may be configured tochange or convert an outer surface of a leach particle from a primarymetal sulfide (e.g., chalcopyrite) to a metastable non-stoichiometricbinary metal sulfide phase which differs from chalcopyrite andcovellite. In some embodiments, a reductive activation step, maycompletely or partially modify, disturb, damage, or alter the crystallattice sufficiently to enhance the oxidative dissolution processwhereby the leach time to reach approximately 95% metal recovery can beachieved in about 6 hours or less.

In some instances, chalcopyrite leach particles may undergo a reductiveactivation/reductive pre-treatment step in the one or more reductiveleach reactors 220, wherein at least a portion of the outer surfaceproduct layers of the chalcopyrite leach particles may be at leastpartially transformed to a transitionary mineral phase comprising ametastable non-stoichiometric binary metal sulfide phase, wherein thechalcopyrite leach particles are not fully converted to a secondarymetal sulfide phase such as covellite. For example, less than about halfof each particle may be converted to said transitionary mineral phase,and more preferably, less than about 10% of each particle, but more than50% of each particle outer surface may be converted to saidtransitionary mineral phase, and therefore, residence time of the metalsulfide concentrate 116 within the reductive activation process may bekept to a minimum.

In some instances, the activation may require conversion of 0.01 to 50%of the primary sulfide; or alternatively may require conversion of 0.01to 40% of the primary metal sulfide; or alternatively may requireconversion of 0.01 to 30% of the primary sulfide; or alternatively mayrequire conversion of 0.01 to 20% of the primary sulfide; oralternatively may require conversion of 0.01 to 10% of the primarysulfide; for example conversion of as little as 2 to 8% of the primarysulfide. The extent of conversion to a metastable non-stoichiometricbinary metal sulfide phase is carried out so as to introduce pointdefects substantially throughout the entirety of the activated particle.

Redox potential may, in some instances, vary within the reductiveactivation process as a function of time or within various reductiveleach reactors 220. In some instances, the reductive process maycomprise a different pH than a pH maintained during the subsequentoxidative leach. In some instances, the reductive activation maycomprise a different redox potential than the subsequent oxidativeleach. For example, the measured redox potential within the activationcircuit 220 may fall within the range of approximately 200 mV (SHE) toabout 650 mV (SHE), wherein portions of the chalcopyrite leach particlesmay be converted to a transitionary, mineral phase comprising ametastable, non-stoichiometric binary metal sulfide phase. Measuredredox potential within the oxidative leach circuit, may fall within therange of approximately 600 mV (SHE) to about 800 mV (SHE). These redoxpotentials may change or fluctuate with time or depending on thecomposition of concentrate and/or the metal value desired to berecovered from the concentrate.

In some embodiments, the metal sulfide concentrate 116 (e.g., coppersulfide concentrate) may comprise residual flotation reagents. In somepreferred embodiments, the metal sulfide comprises copper in the form ofChalcopyrite (CuFeS₂), and/or Covellite (CuS). However, it should beknown that other metal-bearing minerals occurring in combination withmetal sulfides (e.g., including Acanthite Ag₂S, Chalcocite Cu₂S, BorniteCu₅FeS₄, Enargite Cu₃AsS₄, Tennantite Cu₁₂As₄S₁₃, TetrahedriteCu₃SbS₃.x(Fe, Zn)₆Sb₂S₉, Galena PbS, Sphalerite ZnS, ChalcopyriteCuFeS₂, Pyrrhotite Fe_(1-x)S, Millerite NiS, Pentlandite (Fe,Ni)₉S₈,Cinnabar HgS, Realgar AsS, Orpiment As₂S₃, Stibnite Sb₂S₃, Pyrite FeS₂,Marcasite FeS₂, Molybdenite MoS₂, Malachite CuCO₃.Cu(OH)₂, Azurite2CuCO₃.Cu(OH)₂, Cuprite Cu₂O, Chrysocolla CuO.SiO₂.2H₂O) may be usedwith the disclosed systems and methods.

In some embodiments, portions of the atmospheric or substantiallyatmospheric metal sulfide leach circuit 200, such as the plurality ofoxidative leach reactors 202, may be maintained below a pH of about 1.8(e.g., between a pH of 0.5 and a pH of about 1.2).

In some preferred embodiments, the atmospheric or substantiallyatmospheric metal sulfide leach 200 may be maintained at a temperaturewhich is below the melting point of elemental sulfur, to controlpassivation of the leaching particles.

It should be known that the particular features, processes, and benefitswhich are shown and described herein in detail are purely exemplary innature and should not limit the scope of the invention. For example,where used herein, and in related co-pending applications referencedherein, the term “atmospheric leach” may comprise leaching under verysmall amounts of pressure which are close, but not exactly, ambient. Inother words, while it is most preferred that “atmospheric” leaching isperformed completely open to air, it is anticipated by the inventorsthat some best modes of leaching using the inventive concepts mayincorporate the use of a plurality of stirred-tank reactors 202 whichare open to air, and one or more smaller shear-tank reactors 212 whichmay be pressurizable (e.g., to 1-10 bar) to overcome oxygen transferlimitations. Accordingly, portions of the oxidative metal sulfide leach200 may be performed under slight pressure (e.g., in a covered orpressurizable vessel) or completely atmospherically (e.g., in aplurality of non-pressurized stirred-tank reactors).

It is further anticipated that in preferred embodiments, most (e.g., upto approximately 95%) of the cumulative oxidative leach time of a metalsulfide leach particle may occur at atmospheric conditions, while lessthan approximately 10% of the cumulative oxidative leach time may occurat or above atmospheric conditions, giving rise to the term“substantially atmospheric” used throughout this description.

Without departing from the intent of the invention, reductive and/oroxidative reactor head space may be atmospheric or alternativelypressurized to above ambient pressure to enhance oxygen mass transfer.The pressure may be controlled by temperature and/or by an applied gaspressure that is above ambient pressure. It is anticipated thatabove-atmospheric pressures, where/if used, may approach as much as 20bar, but are preferably kept between about 1 bar and about 10 bar, forexample, approximately 5 bar, without limitation.

Although the invention has been described in terms of particularembodiments and applications, one of ordinary skill in the art, in lightof this teaching, can generate additional embodiments and modificationswithout departing from the spirit of or exceeding the scope of theclaimed invention. Accordingly, it is to be understood that the drawingsand descriptions herein are proffered by way of example to facilitatecomprehension of the invention and should not be construed to limit thescope thereof.

What is claimed is:
 1. A method of improving metal leach kinetics andrecovery during atmospheric or substantially atmospheric leaching of ametal sulfide, the method comprising: (a) producing a metal sulfideconcentrate comprising chalcopyrite, via flotation; (b) processing themetal sulfide concentrate in one or more reductive activation reactorswhich are held at a first redox potential, to produce areductively-activated metal sulfide concentrate via a copper metathesisreaction; and, (c) subsequently processing the reductively-activatedmetal sulfide concentrate in an oxidative leach process to extract andrecover metal values; wherein the reductively-activated metal sulfideconcentrate comprises activated particles comprising chalcopyrite and atransitory, metastable non-stoichiometric binary metal sulfide phasewith point defects substantially throughout the entirety of theactivated particles.
 2. A method of improving metal leach kinetics andrecovery during atmospheric or substantially atmospheric leaching of ametal sulfide, the method comprising: (a) producing a metal sulfideconcentrate comprising chalcopyrite particles via flotation; (b)processing the metal sulfide concentrate in one or more reductiveactivation reactors which are held at a first redox potential, toproduce a reductively-activated metal sulfide concentrate via a coppermetathesis reaction; and, (c) subsequently processing thereductively-activated metal sulfide concentrate in an oxidative leachprocess to extract and recover metal values; wherein thereductively-activated metal sulfide concentrate comprises convertedchalcopyrite particles having a transitionary metastablenon-stoichiometric binary metal sulfide mineral phase which differs fromcovellite.
 3. A method of improving metal leach kinetics and recoveryduring atmospheric or substantially atmospheric leaching of a metalsulfide, the method comprising: (a) producing a metal sulfideconcentrate via flotation; (b) processing the metal sulfide concentratein one or more reductive activation reactors which are held at a firstredox potential, to produce a reductively-activated metal sulfideconcentrate via a copper metathesis reaction; and, (c) subsequentlyprocessing the reductively-activated metal sulfide concentrate in anoxidative leach process to extract and recover metal values; whereinstep (c) comprises moving the reductively-activated metal sulfideconcentrate from a plurality of oxidative stirred-tank reactors to oneor more shear-tank reactors.
 4. The method of claim 3, wherein theplurality of oxidative stirred-tank reactors are in series with said oneor more shear-tank reactors.
 5. The method of claim 3, wherein theplurality of oxidative stirred-tank reactors are in parallel with saidone or more shear-tank reactors.
 6. A method of improving metal leachkinetics and recovery during atmospheric or substantially atmosphericleaching of a metal sulfide, the method comprising: (a) producing ametal sulfide concentrate comprising chalcopyrite via flotation; (b)processing the metal sulfide concentrate in one or more reductiveactivation reactors which are held at a first redox potential, toproduce a reductively-activated metal sulfide concentrate via a coppermetathesis reaction; and, (c) subsequently processing thereductively-activated metal sulfide concentrate in an oxidative leachprocess to extract and recover metal values; wherein step (b) involvesconverting less than about 10 wt. % or less than about 10 vol. % ofchalcopyrite within the metal sulfide concentrate, to a metastablenon-stoichiometric binary metal sulfide mineral phase.
 7. A method ofextracting a metal from a metal sulfide particle, comprising: activatinga metal sulfide particle comprising chalcopyrite, by changing a portionof the metal sulfide particle from chalcopyrite to a non-stoichiometric,metastable binary metal sulfide phase to introduce point defectssubstantially throughout the entirety of the activated metal sulfideparticle; and extracting copper from the activated metal sulfideparticle.
 8. The method of claim 7, wherein extracting copper from theactivated metal sulfide particle comprises an oxidative leachingprocess.
 9. The method of claim 7, wherein the portion of the metalsulfide particle changed to a non-stoichiometric, metastable binarymetal sulfide phase is less than about one tenth of the metal sulfideparticle by weight or less than about one tenth by volume.
 10. Themethod of claim 7, wherein activating the metal sulfide particle isperformed in a reductive environment ranging from about 200 to about 650mV (Standard Hydrogen Electrode).
 11. A method of leaching a metalsulfide concentrate, comprising: processing a metal sulfide concentratein a reactor at a first redox potential to produce areductively-processed metal sulfide concentrate comprising an activatedparticle having a non-stoichiometric metastable binary metal sulfidephase with point defects introduced substantially throughout theentirety of the activated particle; and leaching a metal from thereductively-processed metal sulfide concentrate via oxidativedissolution; wherein the oxidative dissolution occurs in an oxidativeleach reactor at a second redox potential which is greater than a restpotential of the activated particle.
 12. The method of claim 11, whereinthe non-stoichiometric metastable binary metal sulfide phase comprisesless than about 10 wt. % or less than about 10 vol. % of the activatedparticle.
 13. The method of claim 11, wherein the first redox potentialranges from about 200 to about 650 mV (Standard Hydrogen Electrode). 14.The method of claim 11, wherein the second redox potential ranges fromabout 600 to about 750 mV (Standard Hydrogen Electrode).
 15. The methodof claim 11, wherein the metal sulfide concentrate compriseschalcopyrite.
 16. The method of claim 11, wherein the metal leached fromthe metal sulfide concentrate is copper.
 17. A method of extracting ametal from a metal sulfide particle, comprising: activating a metalsulfide particle comprising chalcopyrite, by changing less than about 10wt. % or less than about 10 vol. % of the metal sulfide particle from aprimary metal sulfide to a binary metal sulfide phase; and extractingcopper from the activated metal sulfide particle by an oxidative leachprocess.
 18. The method of claim 17, wherein the binary metal sulfidephase comprises a non-stoichiometric metastable binary metal sulfidephase with point defects substantially throughout the entirety of theactivated metal sulfide particle.
 19. A method of leaching a metalsulfide concentrate, comprising: processing a metal sulfide concentratein a reactor at a first redox potential to produce areductively-processed metal sulfide concentrate comprising an activatedparticle having a non-stoichiometric metastable binary metal sulfidephase with point defects introduced substantially throughout theentirety of the activated particle; and leaching a metal from thereductively-processed metal sulfide concentrate via oxidativedissolution; wherein the second redox potential ranges from about 600 toabout 750 mV (Standard Hydrogen Electrode).